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selftests/mm: replace atomic_bool with pthread_barrier_t

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Patch series "selftests/mm: fix deadlock after pthread_create".

On Android arm, pthread_create followed by a fork caused a deadlock in the
case where the fork required work to be completed by the created thread.

Update the synchronization primitive to use pthread_barrier instead of
atomic_bool.

Apply the same fix to the wp-fork-with-event test.


This patch (of 2):

Swap synchronization primitive with pthread_barrier, so that stdatomic.h
does not need to be included.

The synchronization is needed on Android ARM64; we see a deadlock with
pthread_create when the parent thread races forward before the child has a
chance to start doing work.

Link: https://lkml.kernel.org/r/20241003211716.371786-1-edliaw@google.com
Link: https://lkml.kernel.org/r/20241003211716.371786-2-edliaw@google.com
Fixes: cff2945827 ("selftests/mm: extend and rename uffd pagemap test")
Signed-off-by: Edward Liaw <edliaw@google.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Edward Liaw 2024-10-03 21:17:10 +00:00 committed by Andrew Morton
parent 963a7f4d3b
commit e61ef21e27
3 changed files with 12 additions and 10 deletions
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5
tools/testing/selftests/mm/uffd-common.c
View file

@ -18,7 +18,7 @@ bool test_uffdio_wp = true;
unsigned long long *count_verify;
uffd_test_ops_t *uffd_test_ops;
uffd_test_case_ops_t *uffd_test_case_ops;
atomic_bool ready_for_fork;
pthread_barrier_t ready_for_fork;
static int uffd_mem_fd_create(off_t mem_size, bool hugetlb)
{
@ -519,7 +519,8 @@ void *uffd_poll_thread(void *arg)
pollfd[1].fd = pipefd[cpu*2];
pollfd[1].events = POLLIN;
ready_for_fork = true;
/* Ready for parent thread to fork */
pthread_barrier_wait(&ready_for_fork);
for (;;) {
ret = poll(pollfd, 2, -1);

3
tools/testing/selftests/mm/uffd-common.h
View file

@ -33,7 +33,6 @@
#include <inttypes.h>
#include <stdint.h>
#include <sys/random.h>
#include <stdatomic.h>
#include "../kselftest.h"
#include "vm_util.h"
@ -105,7 +104,7 @@ extern bool map_shared;
extern bool test_uffdio_wp;
extern unsigned long long *count_verify;
extern volatile bool test_uffdio_copy_eexist;
extern atomic_bool ready_for_fork;
extern pthread_barrier_t ready_for_fork;
extern uffd_test_ops_t anon_uffd_test_ops;
extern uffd_test_ops_t shmem_uffd_test_ops;

14
tools/testing/selftests/mm/uffd-unit-tests.c
View file

@ -774,7 +774,7 @@ static void uffd_sigbus_test_common(bool wp)
char c;
struct uffd_args args = { 0 };
ready_for_fork = false;
pthread_barrier_init(&ready_for_fork, NULL, 2);
fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
@ -791,8 +791,9 @@ static void uffd_sigbus_test_common(bool wp)
if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
err("uffd_poll_thread create");
while (!ready_for_fork)
; /* Wait for the poll_thread to start executing before forking */
/* Wait for child thread to start before forking */
pthread_barrier_wait(&ready_for_fork);
pthread_barrier_destroy(&ready_for_fork);
pid = fork();
if (pid < 0)
@ -833,7 +834,7 @@ static void uffd_events_test_common(bool wp)
char c;
struct uffd_args args = { 0 };
ready_for_fork = false;
pthread_barrier_init(&ready_for_fork, NULL, 2);
fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
if (uffd_register(uffd, area_dst, nr_pages * page_size,
@ -844,8 +845,9 @@ static void uffd_events_test_common(bool wp)
if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
err("uffd_poll_thread create");
while (!ready_for_fork)
; /* Wait for the poll_thread to start executing before forking */
/* Wait for child thread to start before forking */
pthread_barrier_wait(&ready_for_fork);
pthread_barrier_destroy(&ready_for_fork);
pid = fork();
if (pid < 0)